The work described in this proposal seeks to further our understanding of the neural mechanisms underlying impulsivity, and their modulation by social influences. Impulsivity lies at the heart of a large number of maladaptive behaviors, ranging from ones common in every day life (e.g., bad eating habits, and failures to adequately save) to ones closely associated with clinical disorders such as drug addiction, ADHD and aggressive behavior. The propensity for impulsivity varies substantially over the life cycle, as does its susceptibility to social influences (such as authority figures, peer-pressure, and advertising). We will study impulsivity in the context of intertemporal decision making. Intertemporal decisions involve choices between two rewards available at different times. It is well recognized that people discount rewards more steeply over the near term than over longer terms. That is, rewards that are available immediately have disproportionately high value to us, and delaying them (e.g., by a week) devalues rewards substantially more than when a similar delay is imposed on future rewards (e.g., from one week to two weeks). One explanation for this behavior is that human discounting involves two separate systems, one that heavily devalues the future, and another that is more sensitive to future reward. In previous work, we have found evidence that distinguishable neural mechanisms may be associated with each of these systems, and that their relative activity correlates with the choices that people make between immediate and future rewards. In this proposal, we will conduct studies to refine our understanding of these neural mechanisms, their relationship to intertemporal choice, to individual differences in impulsivity, and their modulation by social influences. Under our first two aims, we seek to manipulate each system individually, in an effort to isolate the contributions that each makes to intertemporal choice. Under a third aim, we will examine the influence that social factors have on the functioning of these mechanisms, in an effort to better understand the mechanisms that mediate social influences on impulsive behavior. An understanding of the neural mechanisms underlying impulsivity, and how these are impacted by social influences, promises to provide insights that will be useful in designing interventions, both at the individual and social levels that better mitigate the costs of impulsivity to the individual and society. [unreadable] [unreadable] [unreadable]